The present invention relates to an automatically focusing system and the focusing method therefor, and more particularly to an automatically focusing system and the focusing method therefor which are to be applied to picture image inputting equipment such as video camera, and digital still camera wherein an imaging device is used.
In recent years, reduction in the number of parts to be used becomes an important problem as a result of request for low cost with progress in a serious situation in digital still camera market. Under the circumstances, one of major parts in digital still camera is microprocessor (including DSP). In this respect, while a microprocessor of late date has a low price, it exhibits performance superior to that required for functioning as a controller of a digital still camera. For this reason, there is a tendency wherein, for example, function in a part of distance measuring module (AF sensor) in silver halide camera is replaced by imaging system+digital signal processing in digital still camera. As focusing manners in digital still camera, there are major manners of xe2x80x9cexplanatory methodsxe2x80x9d and xe2x80x9ccorrelationxe2x80x9d. In this connection, both the xe2x80x9cexplanatory methodxe2x80x9d and xe2x80x9ccorrelationxe2x80x9d manners will be described hereinafter.
In a focusing method according to xe2x80x9cexplanatory methodxe2x80x9d manner known in general, although an AF evaluated value (calculated from a high frequency component of a picture image) at a position where the picture image has been taken into a camera can be obtained. It is difficult to detect such a fact that where is a focusing point in either direction of before or after the intake position of the picture image as well as such a fact that where is a focusing point with how much magnitude of a distance. For this reason, AF evaluated values ranging over the whole area where lens transfers are required in order to detect the focusing point with avoidance of the maximal point. Accordingly, there is such a problem that the number of times for photographing an amount corresponding to the whole area becomes necessary, and an operation for returning a resulting value up to a position of the focusing point is added thereto, so that a certain time is required for obtaining a correct focusing position.
As to xe2x80x9ccorrelation mannerxe2x80x9d, there are autocorrelation manner and cross-correlation manner. First, in a focusing method according to autocorrelation manner, luminous flux of two or more different patterns are taken into one frame. Focus information can be obtained from picture images which have been taken into a camera an amount of which corresponds to that of one frame, while it results in a very high peak value at a position of origin (focusing point) of autocorrelation coefficient, since the correlation is derived from the same data. Consequently, since AF information submerges due to the peak value in the vicinity of a focusing point, it becomes difficult to detect such focusing point in the vicinity thereof. Thus, there is such a problem that a focusing point must be detected in accordance with another manner in the vicinity of focusing point.
On the other hand, respective AF areas are imaged with respect to luminous flux of two different patterns in a focusing method according to cross-correlation manner, but it is required to prepare two image memories, while no very high peak value is obtained at a position of origin as in autocorrelation manner. From the fact described hereinbefore, focus information can be obtained over a range extending from the vicinity of focusing point to a position away therefrom without being submerged by such peak value. In cross-correlation manner, however, luminous flux of two different patterns must be prepared by means of an AF diaphragm plate in order to obtain focus information, so that there is such a problem that the AF diaphragm plate becomes unnecessary at the time of taking photograph. In addition, there is also such a problem that a size of opening is fixed in AF diaphragm plate and as a result, it is difficult to optimize quantity of light which has been received by an image sensor.
Furthermore, a method for detecting a focusing point by utilizing chromatic aberration of an object in a video camera of a multiple plate type has been also proposed. For instance, xe2x80x9can image pickup apparatusxe2x80x9d described in Japanese Patent Application Laid-Open (JP-A) No. 07-084177 is the image pickup apparatus wherein luminous flux from photographing lenses is decomposed into light of the plurality of colors through an optical system for color decomposition, and then an object image based on the light of respective colors is introduced to corresponding image pickup means, respectively, characterized by that one of the plurality of image pickup means is used as a reference image pickup means at least a part of the photographing lenses is driven in such that the object image is focused to the reference image pickup means, and thereafter signals from the image pickup means other than the reference image pickup means are allowed to input to a focus detecting means, whereby a position on optical axis is established by utilizing the signals from the focus detecting means.
In the xe2x80x9cimage pickup apparatusxe2x80x9d described in the above Japanese Patent Application Laid-Open (JP-A) No. 07-084177, however, since a distance up to focusing point has not been detected, very often image pickup operations are required for obtaining the focusing point until it is achieved, and thus, there is such a problem that a certain time is required for attaining a pertinent position of the focusing point as in the above-mentioned xe2x80x9cexplanatory methodsxe2x80x9d manner.
It is an object of the present invention to provide an automatically focusing system wherein an imaging device of a multiple plate type is used, characterized by having a simple construction and by which high-speed focusing operation becomes possible as well as to provide the focusing method therefor.
In order to solve the above described problems, the invention according to a first aspect relates to an automatically focusing system provided with an imaging device of a multiple plate type, comprising a lens system for subjecting object light ray to chromatic aberration correction to image the resulting light ray; a color decomposing means for separating the object light ray through the lens system into respective color components; a plurality of imaging devices in each of which an AF area is established in a central part of an imaging area and which is served for receiving the color component to convert the same into picture image data; a focusing position estimating means for calculating defocusing characteristic information of the picture image data in the respective AF areas of the plurality of imaging devices which have been disposed in such that light receiving distances differ from one another in every respective colors to estimate a distance up to a focusing point as well as a direction along the same on the basis of the defocusing characteristic information of the calculated respective colors; a focusing condition discriminating means for judging whether or not a situation is in a focusing condition based on the distance up to the focusing point estimated by the focusing position estimating means; and a driving means for shifting the lens system or the color decomposing means by the distance up to the focusing point along the direction in the focusing point estimated by the focusing position estimating means in the case when it was judged that a situation was not in a focusing condition by means of the focusing condition discriminating means.
Furthermore, the invention according to a second aspect relates to an automatically focusing system provided with imaging devices of a multiple plate type, comprising a lens system for subjecting object light ray to chromatic aberration correction to image the resulting light ray; a color decomposing means for separating the object light ray through the lens system into respective color components; a plurality of imaging devices in each of which an AF area is established in a central part of an imaging area and which is served for receiving the color component to convert the same into picture image data; an imaging device shifting means for shifting the imaging devices; a focusing position estimating means for calculating defocusing characteristic information of the picture image data in the respective AF areas of the plurality of imaging devices which have been shifted by the imaging device shifting means in such that light receiving distances differ from one another in every respective colors and calculating point image radii in the respective colors on the basis of point image distribution factors of the respective colors calculated to estimate a distance up to a focusing point as well as a direction along the same based on the point image radii of the calculated respective colors; a focusing condition discriminating means for judging whether or not a situation is in a focusing condition based on the distance up to the focusing point estimated by the focusing position estimating means; and a driving means for shifting the lens system or the color decomposing means by the distance up to the focusing point along the direction in the focusing point estimated by the focusing position estimating means in the case when it was judged that a situation was not in a focusing condition by means of the focusing condition discriminating means.
Furthermore, the invention according to a third aspect relates to an automatically focusing system in the first or second aspect, wherein the focusing position estimating means multiplies the picture image data in the AF area by window function, then subjects the result to two-dimensional Fourier transform to transform the result into an amplitude and a phase in a frequency region thereby to replace respective phases in the whole frequency region with zero, and thereafter subjects the result to two-dimensional inverse Fourier transform to calculate the point image distribution factor.
Moreover, the invention according to a fourth aspect relates to an automatically focusing system in the second or third aspect, wherein the focusing position estimating means calculates a sectional area based on a threshold value calculated on the basis of a peak value of its origin of the point image distribution factor, and the point image radius is calculated on the basis of the calculated sectional area.
Furthermore, the invention according to a fifth aspect relates to a focusing method for an automatically focusing system, comprising a first step for disposing a plurality of imaging devices in such that respective light receiving distances differ from one another; a second step for subjecting object light ray to chromatic aberration correction by means of a lens system to image the resulting light ray; a third step for separating the object light ray through the lens system into respective color components; a fourth step for estimating a distance up to a focusing point as well as a direction along the same on the basis of point image distribution radii in respective colors calculated wherein light rays in respective color components are received by the plurality of imaging devices, point image distribution factors indicating defocusing characteristics in every respective colors of the picture image data in the respective AF areas are calculated respectively, and the point image radii of the respective colors are calculated on the basis of the calculated point image distribution factors in the respective colors; a fifth step for judging whether or not a situation is in a focusing condition based on the estimated distance up to the focusing point; a sixth step for shifting the lens system or the color decomposing means by the distance up to the focusing point along the direction in the focusing point estimated in the case when it was judged that a situation was not in a focusing condition in the fifth step; a seventh step for repeating the second step through the fifth step after shifting the lens system or the color decomposing means by the distance up to the focusing point along the direction in the focusing point estimated; and an eighth step for performing normal photographing operation after shifting the plurality of imaging devices to positions wherein the respective distances for receiving light rays are identical with each other in the case when it was judged that a situation was in a focusing condition in the fifth step.
Moreover, the invention according to a sixth aspect relates to a focusing method for an automatically focusing system in the fifth aspect, wherein in the fourth step, the picture image data in the AF area is multiplied by window function, then the result is subjected to two-dimensional Fourier transform to transform into an amplitude and a phase in a frequency region, the respective phases in the whole frequency region are replaced by zero, and thereafter, the result is subjected to two-dimensional inverse Fourier transform to calculate the point image distribution factor.
Furthermore, the invention according to a seventh aspect relates to a focusing method for an automatically focusing system in the fifth or sixth aspect, wherein in the fourth step, a sectional area is calculated on the basis of a threshold value calculated based on a peak value in its origin of the point image distribution factor, and the point image radii are calculated on the basis of the calculated sectional area.